1. Field of the Invention
The present invention relates to a control apparatus regulating charging/discharging power of an electricity accumulation mechanism, and particularly, to a control apparatus of an electricity accumulation mechanism adjusting regulation in accordance with a deterioration degree of the electricity accumulation mechanism.
2. Description of the Background Art
Recently, hybrid cars, fuel-cell vehicles and electric vehicles running by the drive power from a motor are attracting attention as a measure against environmental problems. To such a vehicle, a capacitor (condenser) or a battery (secondary cell) is mounted in order to accumulate power to be supplied to the motor. Such a capacitor or battery has a property that it deteriorates by loads and that the performance is impaired. Techniques for regulating charging/discharging power in accordance with a deterioration degree have been proposed, so that such deterioration is suppressed and the lifetime is increased.
Japanese Patent Laying-Open No. 7-255133 discloses a charging/discharging control apparatus for a secondary cell, which is capable of alleviating gradual increase in a deterioration rate of the capacitance and securing a long lifetime, even with a secondary cell having a prolonged history. The charging/discharging control apparatus disclosed in Japanese Patent Laying-Open No. 7-255133 is a charging/discharging control apparatus for a secondary cell. The charging/discharging control apparatus includes a discharge control unit stopping discharging if the voltage of the secondary cell becomes lower than a prescribed reference value when the secondary cell is discharged, a charge control unit stopping charging if the voltage of the secondary cell becomes higher than a prescribed reference value when the secondary cell is charged, and a history estimation unit estimating the history of the secondary cell based on the state of the secondary cell. The discharge control unit is configured to correct the reference value for stopping discharging to be raised in accordance with a history estimation value by the history estimation unit, while the charge control unit is configured to correct the reference value for stopping charging to be decreased in accordance with a history estimation value by the history estimation unit.
According to the invention disclosed by the publication, the history estimation unit estimates the history based on the state of the secondary cell, the discharge control unit corrects the reference voltage value stopping discharging so as to increase in accordance with the history, and the charge control unit correct the reference voltage value stopping charging so as to decrease in accordance with the history. Thus, gradual increase in the deterioration rate of the capacitance by the history is alleviated, and the lifetime of the secondary cell is increased.
However, according to the charging/discharging apparatus disclosed in Japanese Patent Laying-Open No. 7-255133, in accordance with history, the reference voltage value stopping discharging is corrected to be increased, while the reference voltage value stopping charging is corrected to be decreased. Accordingly, regulation of the secondary cell is constantly tightened. Therefore, for example even when the vehicle is driven so as to eliminate excessive loads on the electricity accumulation mechanism, i.e., even when the electricity accumulation mechanism is actuated so as to suppress the deterioration degree of the electricity accumulation mechanism, the regulation is tightened. Thus, there has been a problem that the performance of the electricity accumulation mechanism cannot fully be utilized.